Secondary battery

ABSTRACT

A secondary battery having a current interrupt device (CID) between a negative current collecting plate and a case of the secondary battery. The secondary battery includes: an electrode assembly including a positive electrode, a separator, and a negative electrode; a case housing the electrode assembly; a cap assembly coupled to the case for sealing the case; a positive current collecting plate connected to the positive electrode and the cap assembly; an insulator in the case adjacent an end plate of the case; and a negative current collecting plate connected to the negative electrode and the end plate of the case, the end plate being curved convexly toward an inner cavity of the case.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2008-0133808 filed in the Korean IntellectualProperty Office on Dec. 24, 2008, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a secondary battery, and moreparticularly, to a secondary battery having a current interrupt device(CID) between the bottom of a case and a negative current collectingplate.

2. Description of the Related Art

As generally known, a secondary battery can be recharged and discharged,unlike a primary battery. Secondary batteries may be classified intolow-capacity batteries and high-capacity batteries.

For example, a low-capacity secondary battery includes unit batteries,and is mainly used for small portable electronic devices, such ascellular phones, laptop computers, and camcorders, whereas high-capacitybatteries are used as the power supply for driving motors in hybridelectric vehicles and the like. A high-capacity secondary battery formsa battery module by connecting a plurality of unit batteries in the formof a pack, and is used as the power supply for driving motors in hybridelectric vehicles and the like.

Each of the unit batteries includes an electrode assembly including apositive electrode, a separator, and a negative electrode, a case foraccommodating the electrode assembly, and a cap assembly coupled withthe case to seal the case and having an electrode terminal electricallyconnected with the electrode assembly.

For example, in a cylindrical secondary battery, the positive andnegative electrodes in the electrode assembly respectively includenon-coating portions on which an active material is not coated, and thepositive electrode non-coating portion and the negative electrodenon-coating portion are positioned at opposite sides to each other.

A negative current collecting plate is attached to the negativeelectrode non-coating portion, and a positive current collecting plateis attached to the positive electrode non-coating portion. The negativecurrent collecting plate is connected to the case and the positivecurrent collecting plate is connected to the cap assembly to thus drawcurrent to the outside.

When the negative current collecting plate is connected to the case, thecase serves as a negative electrode terminal. When the positive currentcollecting plate is connected to the cap assembly, the cap assemblyserves as a positive electrode terminal. The cap assembly and the caseare coupled with each other in an insulation structure through a gasket.

The cap assembly includes a cap plate, a positive temperature device, avent plate, an insulator, a middle plate, a sub-plate, and a connectingmember that are sequentially provided from the outside. The connectingmember electrically connects the positive current collecting plate andthe middle plate. The vent plate and the sub-plate are connected to eachother by welding, with the insulator and the middle plate interposedtherebetween.

The vent plate forms a vent which is to be connected to the sub-plate,the vent and the sub-plate form a connection portion, and as theconnection portion is formed by welding, they are easily broken anddisconnected when the internal pressure of the battery rises, to thuscut off current. That is, the current interrupt device (CID) is formedbetween the vent plate and sub-plate of the cap assembly.

To this end, the vent plate is provided with notches so that thecircumference of the vent has a smaller thickness than other portions ofthe vent plate have. However, such a cap assembly interrupts currentwhile the vent is separated as the notches are ruptured by explosion inthe event of an increase of the internal pressure of the battery.

In this manner, the current interrupt device cuts off current afterexplosion, so that the current interrupt device is not able to properlyprevent the explosion of the battery. Moreover, the sub-plate formingthe connection portion together with the vent is formed in a plateshape, and hence there is a large dispersion of an operating pressure,i.e., separation pressure, at which the connection portion of thesub-plate and the vent is disconnected.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a secondary batterywhich can effectively serve to prevent explosion since current isinterrupted by the disconnection of a connection portion beforeexplosion.

The embodiments of the present invention provide a secondary batterywhich can reduce the dispersion of the operating pressure of adisconnection portion since the connection portion can be designed so asto be disconnected under a predetermined operating pressure.

The embodiments of the present invention provide a secondary batterywhich improves reliability with respect to current interruption becausea disconnected state of the connection portion is firmly maintained evenwhen the internal pressure of the case decreases again as the connectionportion between a bottom of the case and a negative current collectingplate is disconnected and the bottom of the case is broken outwardly.

A secondary battery according to one exemplary embodiment of the presentinvention includes: an electrode assembly including a positiveelectrode, a separator, and a negative electrode; a case including anend plate and at least one wall extending therefrom defining an innercavity, the case housing the electrode assembly in the inner cavity; acap assembly coupled to the case for sealing the case; a positivecurrent collecting plate including a first side connected to thepositive electrode in the case and a second side connected to the capassembly; an insulator in the case adjacent the end plate; and anegative current collecting plate including a first side connected tothe negative electrode and a second side adjacent the insulator andconnected to the end plate at a connection portion of the end plate,wherein the end plate is curved convexly toward the inner cavity of thecase.

The insulator may include: an external circumferential surface portioncorresponding to an internal circumferential surface of the at least onewall of the case; a planar portion adjacent the negative currentcollecting plate; and a recessed portion curved concavely toward theinner cavity of the case and contacting the end plate, wherein anaperture extends between the planar portion and the recessed portionnear a center of the insulator, and wherein the negative currentcollecting plate is connected to the end plate through the aperture.

The negative current collecting plate may further include a protrudingportion extending toward and connected to the end plate through theaperture of the insulator at the connection portion.

A portion of the insulator may face the end plate and be curved. Theportion of the insulator facing the end plate may contact the end plateand have a curvature corresponding to a curvature of the end plate.

The end plate may be invertible convexly away from the inner cavity ofthe case to provide a separating space between the end plate and thenegative current collecting plate. The end plate may be invertibleconvexly away from the inner cavity of the case to disconnect thenegative current collecting plate from the end plate when an internalpressure in the case is greater than a reference operating pressure.

The end plate may include at least one notch and be collapsible awayfrom the inner cavity of the case at the at least one notch upon anincrease of an internal pressure in the case.

The at least one notch may include at least one outer circumferentialnotch along at least a portion of an outer circumference of the endplate.

The at least one notch may include central notches arranged in a crosspattern at the connection portion of the end plate. The end plate may beconfigured to rupture away from the inner cavity at the central notcheswhen the internal pressure in the case is greater than a rupturingpressure.

The at least one notch may further include at least one innercircumferential notch connecting the central notches in acircumferential direction.

A portion of the insulator may face the end plate and have a polyhedronshape. A portion of the end plate may face and contact the insulator andhave a polyhedron shape.

According to another exemplary embodiment of the present invention, asecondary battery having a current interrupt device between a negativecurrent collecting plate of the secondary battery and a case of thesecondary battery includes: an electrode assembly including a positiveelectrode, a separator, and a negative electrode; a case including anend plate and at least one wall extending therefrom defining an innercavity, the case housing the electrode assembly in the inner cavity; acap assembly coupled to the case for sealing the case; a positivecurrent collecting plate connecting the positive electrode to the capassembly; an insulator adjacent the end plate; and a negative currentcollecting plate connected to the negative electrode and connectable tothe end plate at a connection portion of the end plate, wherein the endplate is curved toward the inner cavity of the case and is connected tothe negative current collecting plate when an internal pressure in thecase is less than a reference operating pressure, and wherein the endplate is curved away from the inner cavity of the case and is configuredto be disconnected from the negative current collecting plate when theinternal pressure in the case is greater than the reference operatingpressure.

In one embodiment, the end plate includes at least one notch and iscollapsible away from the inner cavity of the case at the at least onenotch when the internal pressure in the case is greater than thereference operating pressure.

As set forth above, according to one exemplary embodiment of the presentinvention, the bottom of the case is protruded inward and connected tothe negative current collecting plate at the connection portion throughan aperture of an insulator, and is configured such that the connectionportion is disconnectable to interrupt current before an explosion ofthe case, thereby preventing explosion.

Since the bottom of the case is curved convexly toward the inside of thecase and connected to the negative current collecting plate at theconnection portion, the connection portion can be designed so as to bedisconnected under a predetermined operating pressure, thus reducing thedispersion of the operating pressure of the connection portion.

Even when the internal pressure of the case decreases after the bottomof the case and the negative current collecting plate are disconnectedand the bottom of the case is broken outwardly, the bottom of the caseremains inverted concavely away from the inner cavity of the case, thusfirmly maintaining a disconnected state of the connection portion. As aresult, reliability with respect to current interruption is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional perspective view of a secondary battery accordingto a first exemplary embodiment of the present invention.

FIG. 2 is an exploded sectional view of a current interrupt device ofthe secondary battery of FIG. 1.

FIG. 3 is a bottom view of a case of the secondary battery of FIG. 2.

FIG. 4 is a sectional view showing a connected state when a connectionportion of a current interrupt device is connected.

FIG. 5 is a sectional view showing a disconnected state when theconnection portion of the current interrupt device of FIG. 4 isdisconnected.

FIG. 6 is a sectional view showing a cut away state after the currentinterrupt device of FIG. 4 is disconnected.

FIG. 7 is an exploded sectional view of a current interrupt device of asecondary battery according to a second exemplary embodiment of thepresent invention.

FIG. 8 is a bottom view of a case of the secondary battery of FIG. 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention. Thedrawings and description are to be regarded as illustrative in natureand not restrictive. Like reference numerals designate like elementsthroughout the specification.

FIG. 1 is a sectional perspective view of a secondary battery accordingto a first exemplary embodiment of the present invention. Referring toFIG. 1, the secondary battery according to the first exemplaryembodiment includes an electrode assembly 10, a case 20, a cap assembly30, a positive current collecting plate 40, and a negative currentcollecting plate 50. The case 20 accommodates the electrode assembly 10and an electrolyte.

The electrode assembly 10 includes a positive electrode 11, a separator12, and a negative electrode 13. The electrode assembly 10 is formed bywinding the positive electrode 11, the negative electrode 13, and theseparator 12 of an insulating material disposed therebetween.

In one example, the electrode assembly 10 may be formed in a cylindricalshape. A sector pin 14 is disposed at the center of the cylindricalelectrode assembly 10. The sector pin 14 maintains the cylindrical shapeof the spirally wound electrode assembly 10.

The positive electrode 11 and the negative electrode 13 are made of athin metal foil and form a current collecting body, and includerespective coating portions 11 a and 13 a and non-coating portions 11 band 13 b which are differentiable according to the application orabsence of an active material. That is, the coating portions 11 a and 13a have an active material applied thereto, and the non-coating portions11 b and 13 b do not have an active material applied thereto.

The case 20 has a space in which the electrode assembly 10 is inserted,and may be formed in a cylindrical or rectangular shape which is open atone end. The case 20 is connected to the negative current collectingplate 50, and serves as a negative electrode terminal in the secondarybattery. The case 20 is made of a conductive metal, such as aluminum, analuminum alloy, or nickel-plated steel.

A cap assembly 30 is coupled with the open end of the case 20 through agasket 31 configured to seal the case 20 accommodating the electrodeassembly 10 and the electrolyte. The cap assembly 30 of the presentexemplary embodiment may be provided with a current interrupt device(not shown) or not, as illustrated in FIG. 1.

Before a detailed description of the cap assembly 30 is provided, thepositive current collecting plate 40 will be discussed. The positivecurrent collecting plate 40 is connected to the non-coating portion 11 bof the positive electrode 11 at the cap assembly 30 side to connect thepositive electrode 11 to the cap assembly 30.

The cap assembly 30 includes a cap plate 32 and a sub-plate 33. The capplate 32 is connected to the positive current collecting plate 40, andserves as a positive electrode terminal in the secondary battery. Thecap plate 32 has a terminal 32 a protruding to the outside and a venthole 32 b.

A positive temperature coefficient element 34 is installed between thecap plate 32 and the sub-plate 33. The positive temperature coefficientelement 34 forms or interrupts current flow between the cap plate 32 andthe sub-plate 33. That is, when a preset temperature is exceeded, theelectrical resistance of the positive temperature coefficient element 34increases to a virtually infinite level, thereby stopping the flow ofcharging or discharging current.

The sub-plate 33 is installed inside the cap plate 32 and connected tothe electrode assembly 10. That is, the sub-plate 33 is electricallyconnected to the positive current collecting plate 40 through aconnection member 35.

An insulating member 36 is provided on the positive current collectingplate 40. The insulating member 36 covers the periphery of the positivecurrent collecting plate 40 below a beading portion 21. Hence, thepositive current collecting plate 40 is electrically connected to thecap plate 32 through the connection member 35 and the sub-plate 33.

After the cap assembly 30 is inserted into the case 20, the cap assembly30 is clamped and fixed to the case 20. Hereupon, the beading portion 21and a clamping portion 22 are formed, and the gasket 31 provides anairtight seal between the case 20 and the cap assembly 30.

The negative current collecting plate 50 is connected to a non-coatingportion 13 b of the negative electrode 13 on one side and connected tothe case 20 on the other side. In order to construct a current interruptdevice (CID) between the negative current collecting plate 50 and thecase 20, an insulator 60 is interposed between the negative currentcollecting plate 50 and a bottom 23 of the case 20 to thus electricallyinsulate the negative current collecting plate 50 and the bottom 23 ofthe case 20.

The negative current collecting plate 50 is connected to the bottom 23of the case 20 at a connection portion CP passing through the interposedinsulator 60. For example, the negative current collecting plate 50 maycontact the bottom 23 of the case 20 at the connection portion CP. Uponan increase of the internal pressure of the case 20, the negativecurrent collecting plate 50 is separated from the bottom 23 of the case20 at the connection portion CP to thus interrupt current.

FIG. 2 is an exploded sectional view of the current interrupt device ofFIG. 1. Referring to FIG. 2, that is, the current interrupt device CIDmay be formed by the negative current collecting plate 50 and the bottom23 of the case 20 that are mostly insulated through the insulator 60 andpartly connected through the connection portion CP.

To form the current interrupt device CID, the bottom 23 of the case 20is curved convexly toward the inside of the case 20. Further, the bottom23 of the case 20 is inverted convexly toward the outside of the case 20and forms a separating space SS during a time from immediately after thebottom 23 of the case 20 is separated from the negative currentcollecting plate 50 at the connection portion CP due to an increase ofthe pressure in the case 20 until immediately before the bottom 23 ofthe case 20 is cut away (see FIGS. 4 and 5).

Before further describing the bottom 23 of the case 20, the insulator 60will be described in more detail. The insulator 60 includes an externalcircumferential surface portion 61 corresponding to the internalcircumferential surface of the case 20, a planar portion 62 supportingthe negative current collecting plate 50; a recessed portion 63 formedconcavely and tightly contacting the bottom 23 of the case 20, and athrough hole 64 penetrated at the center of the insulator 60 from theplanar portion 62 to the recessed portion 63.

The recessed portion 63 of the insulator 60 may be curved facing thebottom 23 of the case 20 on a cut surface directed toward the negativecurrent collecting plate 50 from the positive current collecting plate40, i.e., on a vertical section of FIGS. 1 and 2. Further, the recessedportion 63 is curved along the circumferential direction and forms anoverall three-dimensional curved surface.

The negative current collecting plate 50 further includes a protrudingportion 51 connected at the connection portion CP to the bottom 23 ofthe case 20. The protruding portion 51 is connected to the bottom 23 ofthe case 20 through the through hole 64 of the insulator 60. Therefore,the protruding portion 51 has a diameter D for insertion into thethrough hole 64 and a height H for reaching the bottom 23 of the case 20through the through hole 64.

Again, a portion of the bottom 23 of the case 20 that faces and contactsthe recessed portion 63 of the insulator 60 is curved on a cut surfacedirected toward the negative current collecting plate 50 from thepositive current collecting plate 40, i.e., on a vertical section ofFIGS. 1 and 2.

Further, the bottom 23 of the case 20 is curved along thecircumferential direction and forms an overall three-dimensional curvedsurface. Accordingly, the bottom 23 of the case 20 and the recessedportion 63 of the insulator 60 maintain a stable contact and couplingstructure because they have curved surfaces in contact with each other.

The bottom 23 of the case 20 curved convexly toward the inside of thecase 20 and the protruding portion 51 of the negative current collectingplate 50 are connected at the connection portion CP, so that current isinterrupted between the negative current collecting plate 50 and thecase 20 as the bottom 23 of the case 20 is separated from the connectionportion CP upon an increase of the internal pressure of the case 20.

The bottom 23 of the case 20 having an inward convex shape makes clearthe connection to and disconnection from the protruding portion 51,thereby reducing the dispersion of an operating pressure of theconnection portion CP, which disconnects the connection portion CP at aninternal pressure greater than a predetermined operating pressure. Also,the bottom 23 of the case 20 effectively serves to prevent explosionbecause it forms the separating space SS without explosion as it isdisconnected from the connection portion CP.

FIG. 3 is a bottom view of the case 20 of FIG. 2. Referring to FIGS. 2and 3, the bottom 23 of the case 20 is provided with at least one notch24 having a thickness less than the circumferential thickness of thebottom 23 of the case 20. The notch 24 prevents explosion moreeffectively since it is cut away upon an additional increase of theinternal pressure of the case 20 in a state where current is interruptedby the disconnection of the connection portion CP.

For example, the at least one notch 24 includes one or more outercircumferential notches 241 which are formed along the outercircumference on at least part of the outer circumference of the bottom23 of the case 20. The outer circumferential notches 241 may be formedaround the entire circumference of the bottom 23 of the case 20 (notshown), or may be divided by a predetermined length into two (e.g., oneon both sides, as shown in FIG. 3) or more.

FIGS. 4 to 6 are sectional views showing operating states. FIG. 4 showsa state when the connection portion CP of the current interrupt deviceCID is connected, and FIG. 5 shows a state when the connection portionCP is disconnected. The outer circumferential notches 241 induce theinversion of the bottom 23 of the case 20, which is convex toward theinside of the case 20 in a connected operating state, upon an increaseof the internal pressure of the case 20 above a predetermined referencepressure, thereby facilitating inversion of the bottom 23 of the case 20to an outwardly concave position in which the CID is in a disconnectedstate.

FIG. 6 shows a cut away state after the current interrupt device hasdisconnected current flow. Referring to FIG. 6, even though the internalpressure is reduced due to the outer circumferential notches 241inducing inversion of the bottom 23 of the case 20, the separating spaceSS firmly maintains a disconnected state of the bottom 23 of the case 20and the negative current collecting plate 50, thereby improvingreliability with respect to current interruption.

Referring again to FIG. 3, the at least one notch 24 includes one ormore central notches 242 which are formed in a cross pattern at theconnection portion CP of the bottom 23 of the case 20. The centralnotches 242 may be formed over the entire diameter of the bottom 23 ofthe case 20 (not shown), or may be formed in a cross pattern at apredetermined length at the center part of the bottom 23 of the case 20as shown in FIG. 3.

The central notches 242 are able to cut away the center part of thebottom 23 of the case 20 even if they are not inverted from the outercircumferential notches 241. The central notches 242 firmly maintain adisconnected state of the bottom 23 of the case 20 and the negativecurrent collecting plate 50 because they are directed toward the outsideof the case 20 as they are cut away around the connection portion CP,i.e., at the center part of the bottom 23 of the case 20.

The bottom 23 of the case 20 operated as described above may be providedwith either the outer circumferential notches 241 or the central notches242 at the bottom 23 of the case 20, or may be provided with both theouter circumferential notches 241 and the central notches 242, as shownin FIG. 3.

When comparing the following second exemplary embodiment with the firstexemplary embodiment, descriptions of identical or similar componentswill be omitted, and different components will be described.

FIG. 7 is an exploded sectional view of a current interrupt device in asecondary battery according to a second exemplary embodiment of thepresent invention. FIG. 8 is a bottom view of a case of the secondarybattery of FIG. 7.

Referring to FIGS. 7 and 8, a current interrupt device CID2 according tothe second exemplary embodiment is provided within a through hole 64 ofan insulator 260, and where a recessed portion 263 of the insulator 260and a bottom 223 of a case 220 face and contact each other is formed ina polyhedron. A polygonal line of the recessed portion 263 may be shownon a cut surface directed toward the negative current collecting plate50 from the positive current collecting plate 40, i.e., on a verticalsection of FIG. 7.

Further, the recessed portion 263 is formed in a curved line along thecircumferential direction of the bottom 223 of the case 220 to form aplurality of curved surfaces divided at angulated parts of the polygonalline. Accordingly, the bottom 223 of the case 220 and the recessedportion 263 of the insulator 260 are in linear contact with each otherat the angulated parts, and are in surface contact with each other atthe other parts, thereby maintaining a stable contact and couplingstructure.

The bottom 223 of the case 220 includes at least one notch 224 whichfurther includes inner circumferential notches 243 which are formed in acircumferential direction between the central notches 242 and the outercircumferential notches 241. The inner circumferential notches 243 maybe formed in a singular number (not shown), or may be formed in a pluralnumber having a pattern of concentric circles as shown in FIG. 8.

Therefore, the inner circumferential notches 243 are formed byconnecting the central notches 242 in the circumferential direction. Theinner circumferential notches 243 enable the bottom 223 of the case 220to be cut away between the center part and outer circumferential part ofthe bottom 223 of the case 220 even if the outer circumferential notches241 are not inverted. The bottom 223 of the case 220 forms angulatedparts at the at least one notch 224, and comes into contactcorresponding to the angulated parts formed on the recessed portion 263.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A secondary battery comprising: an electrode assembly comprising apositive electrode, a separator, and a negative electrode; a casecomprising an end plate and at least one wall extending therefromdefining an inner cavity, the case housing the electrode assembly in theinner cavity; a cap assembly coupled to the case for sealing the case; apositive current collecting plate comprising a first side connected tothe positive electrode in the case and a second side connected to thecap assembly; an insulator in the case adjacent the end plate; and anegative current collecting plate comprising a first side connected tothe negative electrode and a second side adjacent the insulator andconnected to the end plate at a connection portion of the end plate,wherein the end plate is curved convexly toward the inner cavity of thecase.
 2. The secondary battery of claim 1, wherein the insulatorcomprises: an external circumferential surface portion corresponding toan internal circumferential surface of the at least one wall of thecase; a planar portion adjacent the negative current collecting plate;and a recessed portion curved concavely toward the inner cavity of thecase and contacting the end plate, wherein an aperture extends betweenthe planar portion and the recessed portion near a center of theinsulator, and wherein the negative current collecting plate isconnected to the end plate through the aperture.
 3. The secondarybattery of claim 2, wherein the negative current collecting platefurther comprises a protruding portion extending toward and connected tothe end plate through the aperture of the insulator at the connectionportion.
 4. The secondary battery of claim 1, wherein a portion of theinsulator faces the end plate and is curved.
 5. The secondary battery ofclaim 4, wherein the portion of the insulator facing the end platecontacts the end plate and has a curvature corresponding to a curvatureof the end plate.
 6. The secondary battery of claim 1, wherein the endplate is invertible convexly away from the inner cavity of the case toprovide a separating space between the end plate and the negativecurrent collecting plate.
 7. The secondary battery of claim 6, whereinthe end plate is invertible convexly away from the inner cavity of thecase to disconnect the negative current collecting plate from the endplate when an internal pressure in the case is greater than a referenceoperating pressure.
 8. The secondary battery of claim 1, wherein the endplate comprises at least one notch and is collapsible away from theinner cavity of the case at the at least one notch upon an increase ofan internal pressure in the case.
 9. The secondary battery of claim 8,wherein the at least one notch comprises at least one outercircumferential notch along at least a portion of an outer circumferenceof the end plate.
 10. The secondary battery of claim 8, wherein the atleast one notch comprises central notches arranged in a cross pattern atthe connection portion of the end plate.
 11. The secondary battery ofclaim 10, wherein the at least one notch further comprises at least oneouter circumferential notch along at least a portion of an outercircumference of the end plate.
 12. The secondary battery of claim 10,wherein the end plate is configured to rupture away from the innercavity at the central notches when the internal pressure in the case isgreater than a rupturing pressure.
 13. The secondary battery of claim10, wherein the at least one notch further comprises at least one innercircumferential notch connecting the central notches in acircumferential direction.
 14. The secondary battery of claim 1, whereina portion of the insulator faces the end plate and has a polyhedronshape.
 15. The secondary battery of claim 14, wherein a portion of theend plate faces and contacts the insulator and has a polyhedron shape.16. A secondary battery having a current interrupt device between anegative current collecting plate of the secondary battery and a case ofthe secondary battery, the secondary battery comprising: an electrodeassembly comprising a positive electrode, a separator, and a negativeelectrode; a case comprising an end plate and at least one wallextending therefrom defining an inner cavity, the case housing theelectrode assembly in the inner cavity; a cap assembly coupled to thecase for sealing the case; a positive current collecting plateconnecting the positive electrode to the cap assembly; an insulatoradjacent the end plate; and a negative current collecting plateconnected to the negative electrode and connectable to the end plate ata connection portion of the end plate, wherein the end plate is curvedtoward the inner cavity of the case and is connected to the negativecurrent collecting plate when an internal pressure in the case is lessthan a reference operating pressure, and wherein the end plate is curvedaway from the inner cavity of the case and is configured to bedisconnected from the negative current collecting plate when theinternal pressure in the case is greater than the reference operatingpressure.
 17. The secondary battery of claim 16, wherein the end platecomprises at least one notch and is collapsible away from the innercavity of the case at the at least one notch when the internal pressurein the case is greater than the reference operating pressure.